Make CSSParserContext be garbage collected.

third_party/WebKit/Source/core/css/CSSGroupingRule.cpp

 /*
  * Copyright (C) 2011 Adobe Systems Incorporated. All rights reserved.
  * Copyright (C) 2012 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1. Redistributions of source code must retain the above
  *    copyright notice, this list of conditions and the following
@@ skipping 44 matching lines @@
 
   if (index > m_groupRule->childRules().size()) {
     exceptionState.throwDOMException(
         IndexSizeError,
         "the index " + String::number(index) +
             " must be less than or equal to the length of the rule list.");
     return 0;
   }
 
   CSSStyleSheet* styleSheet = parentStyleSheet();
-  CSSParserContext context(parserContext(), UseCounter::getFrom(styleSheet));
+  CSSParserContext* context =
+      CSSParserContext::create(parserContext(), styleSheet);
   StyleRuleBase* newRule = CSSParser::parseRule(
       context, styleSheet ? styleSheet->contents() : nullptr, ruleString);
   if (!newRule) {
     exceptionState.throwDOMException(
         SyntaxError,
         "the rule '" + ruleString + "' is invalid and cannot be parsed.");
     return 0;
   }
 
   if (newRule->isNamespaceRule()) {
@@ skipping 81 matching lines @@
 }
 
 DEFINE_TRACE(CSSGroupingRule) {
   CSSRule::trace(visitor);
   visitor->trace(m_childRuleCSSOMWrappers);
   visitor->trace(m_groupRule);
   visitor->trace(m_ruleListCSSOMWrapper);
 }
 
 }  // namespace blink